Highly dispersible reinforcing polymeric fibers

ABSTRACT

Synthetic polymer reinforcing fibers provide dispersability and strength in matrix materials such as concrete, masonry, shotcrete, and asphalt. The individual fiber bodies, substantially free of stress fractures and substantially non-fibrillatable, have generally quadrilateral cross-sectional profiles along their elongated lengths. Preferred fibers and matrix materials having such fibers demonstrate excellent finishability in addition to dispersion and toughness properties.

[0001] This is a Continuation-in-part (CIP) of U.S. Ser. No. 09/843,427filed Apr. 25, 2001, which is pending.

FIELD OF THE INVENTION

[0002] The invention relates to fibers for reinforcing matrix materials,and more particularly to a plurality of synthetic polymer fibers havingexcellent dispersibility and reinforcibility properties, and preferablyexcellent finishability, in hydratable cementitious compositions.Individual fiber bodies are elongated and highly bendable, withgenerally quadrilateral cross-sectional profiles, thereby minimizingfiber balling and maximizing fiber bond.

BACKGROUND OF THE INVENTION

[0003] Although fibers of the present invention are suitable forreinforcing various matrix materials, such as adhesives, asphalts,composites, plastics, rubbers, etc., and structures made from these, thefibers that will be described herein are especially suited forreinforcing hydratable cementitious compositions, such as ready-mixconcrete, precast concrete, masonry concrete (mortar), shotcrete,bituminous concrete, gypsum compositions, gypsum- and/or Portlandcement-based fireproofing compositions, and others.

[0004] A major purpose of the fibers of the present invention is toreinforce concrete, e.g., ready-mix, shotcrete, etc., and structuresmade from these. Such matrix materials pose numerous challenges forthose who design reinforcing fibers.

[0005] Concrete is made using a hydratable cement binder, a fineaggregate (e.g., sand), and a coarse aggregate (e.g., small stones,gravel). A mortar is made using cement binder and fine aggregate.Concretes and mortars are hence brittle materials. If a mortar orconcrete structure is subjected to stresses that exceed its maximumtensile strength, then cracks can be initiated and propagated therein.The ability of the cementitious structure to resist crack initiation andcrack propagation can be understood with reference to the “strength” and“fracture toughness” of the material.

[0006] “Strength” relates to the ability of a cement or concretestructure to resist crack initiation. In other words, strength isproportional to the maximum load sustainable by the structure withoutcracking and is a measure of the minimum load or stress (e.g., the“critical stress intensity factor”) required to initiate cracking inthat structure.

[0007] On the other hand, “fracture toughness” relates to the specific“fracture energy” of a cement or concrete structure. This concept refersto the ability of the structure to resist propagation —or widening—of anexisting crack in the structure. This toughness property is proportionalto the energy required to propagate or widen the crack (or cracks). Thisproperty can be determined by simultaneously measuring the load requiredto deform or “deflect” a fiber-reinforced concrete (FRC) beam specimenat an opened crack and the amount or extent of deflection. The fracturetoughness is therefore determined by dividing the area under a loaddeflection curve (generated from plotting the load against deflection ofthe FRC specimen) by its cross-sectional area.

[0008] In the cement and concrete arts, fibers have been designed toincrease the strength and fracture toughness in reinforcing materials.Numerous fiber materials have been used for these purposes, such assteel, synthetic polymers (e.g., polyolefins), carbon, nylon, aramid,and glass. The use of steel fibers for reinforcing concrete structuresremains popular due to the inherent strength of the metal. However, oneof the concerns in steel fiber product design is to increase fiber “pullout” resistance because this increases the ability of the fiber todefeat crack propagation. In this connection, U.S. Pat. No. 3,953,953 ofMarsden disclosed fibers having “J”-shaped ends for resisting pull-outfrom concrete. However, stiff fibers having physical deformities maycause entanglement problems that render the fibers difficult to handleand to disperse uniformly within a wet concrete mix. More recentdesigns, involving the use of “crimped” or “wave-like” polymer fibers,may have similar complications, depending on the stiffness of the fibermaterial employed.

[0009] Polyolefin materials, such as polypropylene and polyethylene,have been used for reinforcing concrete and offer an economic advantagedue to relative lower cost of the material. However, these polyolefinicmaterials, being hydrophobic in nature, resist the aqueous environmentof wet concrete. Moreover, the higher amount of polyolefin fibers neededin concrete to approximate the strength and fracture toughness of steelfiber-reinforced concrete often leads to fiber clumping or “balling” andincreased mixing time at the job site. This tendency to form fiber ballsmeans that the desired fiber dosage is not achieved. The correctconcentration of fibers is often not attained because the fiber ballsare removed (when seen at the concrete surface) by workers intent onachieving a finished concrete surface. It is sometimes the case thatlocations within the cementitious structure are devoid of thereinforcing fibers entirely. The desired homogeneous fiber dispersion,consequently, is not obtained.

[0010] Methods for facilitating dispersion of fibers in concrete areknown. For example, U.S. Pat. No. 4,961,790 of Smith et al. disclosedthe use of a water-soluble bag for introducing a large number of fibersinto a wet mix. U.S. Pat. No. 5,224,774 of Valle et al. disclosed theuse of non-water-soluble packaging that mechanically disintegrated uponmixing to avoid clumping and to achieve uniform dispersal of fiberswithin the concrete mix.

[0011] The dispersal of reinforcing fibers could also be achievedthrough packaging of smaller discrete amounts of fibers. For example,U.S. Pat. No. 5,807,458 of Sanders disclosed fibers that were bundledusing a circumferential perimeter wrap. According to this patent, thecontinuity of the peripheral wrapping could be disrupted by agitationwithin the wet concrete mix, and the fibers could be released anddispersed in the mix.

[0012] On the other hand, World Patent Application No. WO 00/49211 ofLeon (published Aug. 8, 2000) disclosed fibers “packeted” together butseparable when mixed in concrete. A plurality of fibers wereseparably-bound together, such as by tape adhered to cut ends of thefibers, thereby forming a “packet.” Within a wet cementitious mix, thepackets could be made to break and/or dissolve apart to permitseparation and dispersal of individual fibers within the mix.

[0013] The dispersal of reinforcing fibers may also be achieved byaltering fibers during mixing. For example, U.S. Pat. No. 5,993,537 ofTrottier et al. disclosed fibers that progressively fibrillated uponagitation of the wet concrete mix. The fibers presented a “low initialsurface area” to facilitate introducing fibers into the wet mix, and,upon agitation and under the grinding effect of aggregates in the mix,underwent “fibrillation,” which is the separation of the initiallow-surface-area fibrous material into smaller, individual fibrils. Itwas believed that homogeneous fiber distribution, at higher additionrates, could thereby be attained.

[0014] A novel approach was taught in U.S. Pat. No. 6,197,423 of Riederet al., which disclosed mechanically-flattened fibers. For improvedkeying within concrete, fibers were flattened between opposed rollers toattain variable width and/or thickness dimensions and stress-fracturesperceivable through microscope as discontinuities and irregular andrandom displacements of polymer on the surface of the individual fibers.This microscopic stress fracturing was believed to improve bondingbetween cement and fibers, and, because the stress-fractures werenoncontinuous in nature, the fibers were softened to the point at whichfiber-to-fiber entanglement (and hence fiber balling) was minimized oravoided. The mechanical-flattening method of Rieder et al. was differentfrom the method disclosed in U.S. Pat. No. 5,298,071 of Vondran, whereinfibers were interground with cement clinker and retained cementparticles embedded into the surface.

[0015] In this vein, the nature of the fiber surface has also been afrequent topic of research in fiber dispersion and bonding in concrete.For example, U.S. Pat. No. 5,753,368 of Hansen disclosed a list ofwetting agents such as emulsifiers, detergents, and surfactants torender fiber surfaces more hydrophilic and thus more susceptible tomixing in wet concrete. On the other hand, U.S. Pat. No. 5,753,368 ofBerke et al. taught that the bonding between concrete and fibers couldbe enhanced by employing particular glycol ether coatings instead ofconventional wetting agents that tended to introduce unwanted air at thefiber/concrete interface.

[0016] Of course, as mentioned in U.S. Pat. No. 5,298,071 and U.S. Pat.No. 6,197,423 as discussed above, physical deformation of the fibersurface was also believed to improve the fiber-concrete bond. U.S. Pat.No. 4,297,414 of Matsumoto, as another example, taught the use ofprotrusions and ridges to enhance bond strength. Other surfacetreatments, such as the use of embossing wheels to impose patterns onthe fiber, were also used for improving fiber-concrete bond. Fiberdesigners have even bent fibers into sinusoidal wave shapes to increasethe ability of fibers to resist being pulled out from concrete. However,the present inventors realized that increased structural deformations inthe fiber structure may actually enhance opportunities for unwantedfiber balling to occur.

[0017] Against this background, the present inventors see a need fornovel polymeric synthetic reinforcing fibers having ease ofdispersibility in concrete so as to avoid fiber balling and to achieveintended fiber dosage rates, while at the same time to provide strengthand fracture toughness in matrix materials and particularly brittlematerials such as concrete, mortar, shotcrete, gypsum fireproofing, andthe like.

SUMMARY OF THE INVENTION

[0018] In surmounting the disadvantages of the prior art, the presentinvention provides highly dispersible reinforcing polymer fibers, matrixmaterials reinforced by the fibers, and methods for obtaining these.Exemplary fibers of the invention provide ease of dispersibility into,as well as strength and fracture toughness when dispersed within, matrixmaterials, particularly brittle ones such as concrete, mortar, gypsum orPortland cement-based fireproofing, shotcrete, and the like.

[0019] These qualities are achieved by employing a plurality ofindividual fiber bodies having an elongated length defined between twoopposing ends, the bodies having a generally quadrilateralcross-sectional shape along the elongated length of the fiber body. Theindividual fibers thereby have a width, thickness, and length dimensionswherein average width is 1.0-5.0 mm and more preferably 1.3-2.5 mm,average thickness is 0.1-0.3 mm and more preferably 0.15-0.25 mm., andaverage length is 20-100 mm and more preferable 30-60 mm. In preferredembodiments, average fiber width should exceed average fiber thicknessby at least 4 times (i.e., a ratio of at least 4:1) but preferablyaverage width should not exceed average thickness by a factor exceeding50 times (50:1). More preferably, the width to thickness ratio of thefibers is from 5 to 20 (5:1 to 20:1).

[0020] While individual fiber bodies of the invention may optionally beintroduced into and dispersed within the matrix material as a pluralityof separate pieces or separable pieces (i.e. fibers in a scored orfibrillatable sheet, or contained within a dissolvable ordisintegratable packaging, wrapping, packeting, or coating) the fiberscan be introduced directly into a hydratable cementitious compositionand mixed with relative ease to achieve a homogeneous dispersal therein.Individual fiber bodies themselves, however, should not be substantiallyfibrillatable (i.e. further reducible into smaller fiber units) afterbeing subjected to mechanical agitation in the matrix composition to theextent necessary to achieve substantially uniform dispersal of thefibers therein.

[0021] Exemplary individual fiber bodies of the invention are alsosubstantially free of internal and external stress fractures, such asmight be created by clinker grinding or mechanical flattening. Thegeneral intent of the present inventors is to maintain integrity of theindividual fiber bodies, not only in terms of structural fiberintegrity, but also integrity and uniformity of total surface area andbendability characteristic from one batch to the next.

[0022] A generally quadrilateral cross-sectional profile provides ahigher surface area to volume ratio (S_(a)/V) compared to round or ovalmonofilaments comprising similar material and having a diameter ofcomparable dimension. The present inventors believe that a quadrilateralcross-sectional shape provides a better flexibility-to-volume ratio incomparison with round or elliptical cross-sectional shapes, and, moresignificantly, this improved flexibility characteristic translates intobetter “bendability” control. The individual fiber bodies of theinvention will tend to bend predominantly in a bow shape withcomparatively less minimal twisting and fiber-to-fiber entanglement,thereby facilitating dispersion. In contrast, for a given materialelastic modulus and cross-sectional area, the prior art fibers havingcircular or elliptical cross section with major axis/minor axis ratiosof less than 3 will have greater resistance to bending, thereby having agreater tendency for fiber balling when compared to fibers of generallyquadrilateral (e.g., rectangular) cross-section.

[0023] The present inventors further believe that a generallyquadrilateral cross-section will provide excellent fiber surface areaand handability characteristics when compared, for example, to round orelliptical fibers. In this connection, preferred fibers of the inventionhave a “bendability” in the range of 20 (very stiff) to 1300 (verybendable) milli Newton⁻¹*meter⁻² (mN⁻¹*m⁻²), and more preferably in therange of 25 to 500 milli Newton⁻¹*meter⁻². As used herein, the term“bendability” means and refers to the resistance of an individual fiberbody to flexing movement (i.e. to force that is perpendicular to thelongitudinal axis of the fiber) as measured by applying a load to oneend of the fiber and measuring its relative movement with respect to theopposite fiber end that has been secured, such as within a mechanicalclamp or vice, to prevent movement. Thus, a fiber can be called morebendable if it requires less force to bend it to a certain degree. Thebending flexibility of a fiber is a function of its length, shape, thesize of its cross-section, and its modulus of elasticity. Accordingly,the bendability “B” of the fiber is expressed in terms of milliNewton⁻¹*meter⁻² (mN⁻¹*m⁻²) and is calculated using the followingformula $B = \frac{1}{3 \cdot E \cdot I}$

[0024] wherein “E” represents the Young's modulus of elasticity (GigaPascal) of the fiber; and “I” represents the moment of inertia (mm4) ofthe individual fiber body. A fiber having a lower bendability “B” willof course be less flexible than a fiber having a higher bendability “B.”The moment of inertia “I” describes the property of matter to resist anychange in movement or rotation. For a cross-sectional profile having agenerally quadrilateral (or approximately rectangular) shape, the momentof inertia can be calculated using the formula

I _(rectangle)={fraction (1/12)}·w·t ³

[0025] wherein “w” represents the average width of the rectangle and “t”represents the average thickness of the rectangle.

[0026] In further exemplary embodiments, the “bendability” of fibers canbe further improved if the thickness and/or the width of the fibers arevaried along the length of the fibers, for example from 2.5-25 percentmaximum deviation from the average thickness or width value. This smallvariation of the thickness and/or the width of the fiber also improvesthe bond between the reinforcing matrix and the fiber.

[0027] The inventors realized, in view of the above equation for“bendability” “B” of fibers having generally quadrilateralcross-sections, that an increase in the fiber modulus of elasticity “E”will result in a corresponding decrease in bendability and,consequently, make fiber dispersibility more difficult. The inventorsthen realized that to maintain the same level of bendability, the momentof inertia “I” must be decreased, and this could be achieved, forexample, by reducing the thickness of the fibers while maintaining thecross-sectional area of the fibers.

[0028] In further embodiments of the invention, preferred individualfiber bodies have the following properties when measured in thelongitudinal dimension (end to end) along the axis of the fiber body: aYoung's modulus of elasticity of 3-20 Giga Pascals and more preferable5-15 Giga Pascals, a tensile strength of 350-1200 Mega Pascals and morepreferable 400-900 Mega Pascals, and a minimum load carrying capacity intension mode of 40-900 Newtons more preferable 100-300 Newtons.

[0029] A particularly preferred method for manufacturing the fibers isto melt-extrude the polymeric material (e.g., polypropylene as acontinuous sheet); to decrease the temperature of this extruded sheetmelt below ambient temperature (e.g., below 25° C.); to cut or slit thesheet (after cooling) into separate or separable individual fiber bodieshaving generally quadrilateral cross-sections to stretch the individualfibers by at least a factor of 10-20 and more preferably between 12-16,thereby to achieve an average width of 1.0-5.0 mm and more preferably1.3-2.5 mm and an average thickness of 0.1-0.3 mm and more preferably0.15-0.25 mm; and to cut the fibers to obtain individual fiber bodieshaving an average fiber length of 20-100 mm and more preferably between30-60 mm. Further exemplary processes are described hereinafter.

[0030] The present invention is also directed to matrix materials, suchas concrete, mortar, shotcrete, asphalt, and other materials containingthe above-described fibers, as well as to methods for modifying matrixmaterials by incorporating the fibers into the matrix materials.

[0031] Still further exemplary fibers and matrix materials (such asconcrete) having such fibers embedded therein are especially suited forapplications wherein “finishability” is important (such as flooringapplications). The term “finishability” refers to the ability of thefibers to resist “pop-up” from the concrete after its surface has beensmoothed over (i.e. “finshed”). The inventors discovered thatfinishability, similar to dispersion, is a function of fiberbendability, but in addition finishibality is also a function of fiberlength. Exemplary fibers having “finishability” are substantially freeof stress fractures and substantially non-fibrillatable whenmechanically agitated within the matrix material, and they have anaverage bendability of 100 to 2,500, and, more preferably, 150 to 2,000mN⁻¹*m⁻². Preferred fibers with finishability characteristics preferablyhave a Young's modulus of elasticity in the range of 4-20 GigaPascals, atensile strength of 400-1,600 MegaPascals, average width of 1.0-5.0 mm,average thickness of 0.05-0.2 mm, and average length of 20-75 mm,wherein average width exceeds average thickness by a factor of 5-50 andmore preferably by a factor of 7-40.

[0032] Further advantages and features of the invention are furtherdescribed in detail hereinafter.

BRIEF DESCRIPTION OF DRAWING

[0033] An appreciation of the advantages and benefits of the inventionmay be more readily comprehended by considering the following writtendescription of preferred embodiments in conjunction with theaccompanying drawings, wherein

[0034] FIGS. 1-3 are microphotographic enlargements of thecross-sections of PRIOR ART reinforcing fibers;

[0035]FIGS. 4 and 5 are microphotographic enlargements of the generallyquadrilateral cross-sectional profile of exemplary fibers of the presentinvention;

[0036]FIG. 6 is microphotographic enlargement (at 25× magnification) ofthe surface of an exemplary individual fiber body of the presentinvention before mixing in a concrete mixture (which would contain fineand coarse aggregates), and

[0037]FIG. 7 shows the fiber after mixing;

[0038]FIG. 8 is microphotographic enlargement (at 200× magnification) ofthe surface of an exemplary individual fiber body of the presentinvention before mixing in a concrete mixture (which would contain fineand coarse aggregates), and

[0039]FIG. 9 shows the fiber after mixing;

[0040]FIG. 10 is microphotographic enlargement (at 900× magnification)of the surface of an exemplary individual fiber body of the presentinvention before mixing in a concrete mixture (which would contain fineand coarse aggregates), and

[0041]FIG. 11 shows the fiber after mixing;

[0042]FIG. 12 is a microphotographic enlargement (at 900× magnification)of a PRIOR ART fiber mechanically flattened in accordance with U.S. Pat.No. 6,197,423;

[0043]FIG. 13 is a graphic representation of tensile load versus strainbehavior of different fibers;

[0044]FIG. 14 is a graphic representation of tensile stress versusstrain behavior of different fibers;

[0045]FIG. 15 is a photographic of a wedge-splitting device for testingload on cementitious matrix materials containing reinforcing polymerfibers;

[0046]FIG. 16 is a graphic representation of stress vs. crack mouthopening displacement behavior of different fibers; and

[0047]FIG. 17 is a typical stress versus strain curve of a material forpurposes of illustration of principles discussed herein.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0048] The present inventors believe that the reinforcing polymer fibersof the present invention may be used in a variety of compositions andmaterials and structures made from these. The term “matrix materials”therefore is intended to include a broad range of materials that can bereinforced by the fibers. These include adhesives, asphalt, compositematerials (e.g., resins), plastics, elastomers such as rubber, etc., andstructures made therefrom.

[0049] Preferred matrix materials of the invention include hydratablecementitious compositions such as ready-mix concrete, precast concrete,masonry mortar and concrete, shotcrete, bituminous concrete,gypsum-based compositions (such as compositions for wallboard), gypsum-and/or Portland cement-based fireproofing compositions (for boards andspray-application), water-proofing membranes and coatings, and otherhydratable cementitious compositions, whether in dry or wet mix form.

[0050] A primary emphasis is placed upon the reinforcement of structuralconcrete (e.g., ready-mix concrete, shotcrete). However, in general,concrete (whether poured, cast, or sprayed) is an extremely brittlematerial that presents challenges in terms of providing reinforcingfibers that (1) can be successfully introduced into and mixed in thismatrix material and (2) can provide crack-bridging bonding strength inthe resultant fiber reinforced concrete structure.

[0051] Prior to a detailed discussion of the various aforementioneddrawings and further exemplary embodiments of the invention, a briefdiscussion of definitions will be helpful to facilitate a deeperunderstanding of advantages and benefits of the invention. As the fibersof the invention are envisioned for use in the paste portion of ahydratable wet “cement” or “concrete” (terms which may sometimes be usedinterchangeably herein), it is helpful to discuss preliminarily thedefinitions of “cement” and “concrete.” The terms “paste,” “mortar,” and“concrete” are terms of art: pastes are mixtures composed of ahydratable cementitious binder (usually, but not exclusively, Portlandcement, masonry cement, or mortar cement, and may also includelimestone, hydrated lime, fly ash, blast furnace slag, pozzolans, andsilica fume or other materials commonly included in such cements) andwater; mortars are pastes additionally including fine aggregate (e.g.,sand); and concretes are mortars additionally including coarse aggregate(e.g., gravel, stones). “Cementitious” compositions of the inventionthus refer and include all of the foregoing. For example, a cementitiouscomposition may be formed by mixing required amounts of certainmaterials, e.g., hydratable cementitious binder, water, and fine and/orcoarse aggregate, as may be desired, with fibers as described herein.

[0052] Synthetic polymer fibers of the invention comprise at least onepolymer selected from the group consisting of polyethylene (includinghigh density polyethylene, low density polyethylene, and ultra highmolecular weight polyethylene), polypropylene, polyoxymethylene,poly(vinylidine fluoride), poly(methyl pentene),poly(ethylene-chlorotrifluoroethylene), poly(vinyl fluoride),poly(ethylene oxide), poly(ethylene terephthalate), poly(butyleneterephthalate), polyamide, polybutene, and thermotropic liquid crystalpolymers. A preferred synthetic polymer is polypropylene. Exemplaryindividual fiber bodies of the invention may comprise 100%polypropylene, or, as another example, they may comprise predominantlypolypropylene (e.g., at least 70-99%) with the remainder comprisinganother polymer (such as high density polyethylene, low densitypolyethylene) or optional fillers, processing aids, and/or wettingagents, such as are conventionally used in the manufacture of polymerfibers.

[0053] The molecular weight of the polymer or polymers should be chosenso that the polymer is melt processable. For polypropylene andpolyethylene, for example, the average molecular weight can be 5,000 to499,000 and is more preferably between 100,000 to 300,000. Differentgrades of polyethylene may be used, including ones containing branchesand comonomers such as butene, hexene, and octene, and further includingthe so-called “metallocene” polyethylene materials. If polypropylenepolymer is used, it is preferred that no more than about 30 weightpercent polymerized comonomer units or blended resins be present inorder to maintain smooth process operation, with up to about 10% beingpreferred. Propylene homopolymer resins are most preferred, withgeneral-purpose resins in the nominal melt flow range of about 1 toabout 40 grams/10 minutes (ASTM D2497 1995). Preferred resins also haveweight average molecular weight to number average molecular ratios ofabout 2:1 to about 7:1.

[0054]FIG. 1 is a cross-sectional view, originally taken at about 100×magnification, of a PRIOR ART polypropylene fiber with an ellipticalcross-section having dimensions of 0.96 mm in width and 0.63 mm inthickness. The width is close to thickness, and the fiber can twistalmost equally well in all directions about its longitudinal axis.

[0055]FIG. 2 is a cross-sectional view, originally taken at about 100×magnification, of a PRIOR ART elliptical (or oval)-shaped fiber madefrom polyvinylacetate having 0.78 mm width and 0.42 mm thickness.

[0056]FIG. 3 is a cross-sectional view, originally taken at about 100×magnification, of a PRIOR ART fibrillatable fiber commercially availableunder the tradename GRACE® Structural Fibers. This fiber is designed tofibrillate or break into smaller fibrils when mixed in concrete. Thecross-sectional profile resembles a tri-lobed peanut.

[0057]FIG. 4 is a cross-sectional view, originally taken at about 100×magnification, of an exemplary individual fiber body of the presentinvention. The generally quadrilateral cross-sectional profile isevident, in that four sides can be discerned, although the small rightside is not completely straight. The quadrilateral shape could moreaccurately be characterized as trapezoidal in nature, because the longerpair of sides (which define the width) are generally parallel to eachother, while the two smaller sides are somewhat angled with respect tothe longer sides and to each other. The inventors believe that when suchindividual fiber bodies are slit from a larger sheet using cuttingblades, the angle or attitude of the blades can define whether thesmaller sides will have an angle such as in a trapezoid (wherein the twosmaller sides will have different angles), parallelogram (wherein thetwo smaller sides, in addition to the two longer sides, will be parallelto each other), or rectangle (opposing sides are equal, and the anglesare all about 90 degrees).

[0058] The term “quadrilateral” or “generally quadrilateral” as usedherein shall mean and refer to a cross-sectional profile that has foursides, at least two of which are generally parallel to each other anddefine the width dimension of the fiber. The two shorter sides or faces(which therefore define the thickness aspect of the fiber) may or maynot be parallel to each other. The two shorter sides or faces may noteven be straight but could assume, for example, a concave or convexshape if the fibers were extruded as separate bodies rather than beingcut from a sheet.

[0059]FIG. 5 is a partial cross-sectional view, originally taken atabout 200× magnification, of an exemplary individual fiber body of thepresent invention, having 0.19 mm measured thickness. In this enlargedmicrophotograph, the small side is generally perpendicular to the twolonger sides (which are 0.19 mm apart), but there is a slightimperfection at the corners. While sharper corners are preferred,because they are believed by the present inventors to decreasefiber-to-fiber entanglement, some rounding or imperfections due to themanufacturing process are to be expected.

[0060]FIG. 6 is a view, originally at about 25× magnification, of theouter surface of an exemplary individual fiber body of the presentinvention. Exemplary fibers are substantially non-fibrillatable whenmixed and substantially uniformly dispersed in concrete. Accordingly,there are substantially no stress-fractures or discontinuities to beseen in the relatively smooth polymer surface of the fiber, althoughsome surface streaking and imperfections due to the extrusion processand/or slitting process will be seen under magnification. The presentinventors believe that introducing into concrete individual fiber bodiesthat are not mechanically flattened (to the point of havingmicro-stress-fractures over the entire surface) and that are notfibrillatable (reducible into still smaller fibrils when subjected tomechanical agitation in concrete) will lead to more uniform dispersingand reinforcing characteristics, due to uniform fiber surface area tofiber volume ratios and structural integrity from fiber to fiber.Moreover, the surface of the fibers of the invention, upon beingsubjected to mechanical agitation within the aggregate-containingconcrete, will attain a desirable surface roughness that will facilitatebonding of fibers within the concrete matrix when the concrete issolidified.

[0061]FIG. 7 is a view at 25× magnification of the fiber of FIG. 6 afterit has been mixed in concrete for five minutes at twenty-five rpm in atwin shaft mixer (and removed for purposes of illustration herein).Although the fiber surface remains substantially free of micro-stressfractures (e.g., cracks), it will experience a roughening or increasedopacity due to the effect of the aggregate in the concrete mix. At 200×magnification, as shown in FIG. 8, the surface of the fiber, beforebeing introduced into concrete, is substantially free of deformities,the only features being perceived at this level of magnification areslight streaking and imperfections due to the extrusion method used formaking the sheet from which the individual fibers are cut. After beingsubstantially uniformly dispersed in a concrete mix, the fiber, as shownat the same 200× magnification in FIG. 9, does not demonstratesubstantial stress-fracturing or fibrillation. However, a desirablesurface roughening is discernible when viewed at this magnificationlevel. Also, because the polymeric material of the fibers of the presentinvention will be highly oriented, it is not unusual that at highermagnifications there will be evident some small strands sticking outfrom the fiber body, but this can be attributed to having molecularpieces separate from each other, or otherwise to imperfections orscraping and does not constitute substantial fibrillation wherein thefiber body splits into smaller fibril units.

[0062] The polymer fiber surfaces of FIGS. 10-12 were all photographedat about 900× magnification and evidence major differences betweenexemplary fibers of the present invention (FIGS. 10, 11) and amechanically-flattened PRIOR ART fiber (as shown in FIG. 12). FIGS. 10and 11 show the fiber surface, respectively, before and after beingmixed in wet concrete using a twin shaft mixer (having counter-rotatingblades) to attain substantially uniform dispersion of fibers in theconcrete. The extrusion streaking, which is seen in FIG. 10, isdesirably roughened as shown in FIG. 11, but without substantialstress-fracturing or subsurface discontinuities. Even after being mixedin the concrete (which contains sand and coarse aggregate such ascrushed stone or gravel), the surface of the fiber of the presentinvention (FIG. 11) does not develop a micro-stress fractured morphology(e.g., sinewed discontinuities) as seen in the mechanically-flattenedPRIOR ART fiber (FIG. 12), but nevertheless is able to provide adesirably roughened surface and overall integrity as well as to providedesirable bendability characteristics for achieving dispersion of aplurality of individual fiber bodies within the concrete matrix.

[0063] As used herein and above, the terms “plurality” of “individualfiber bodies” refer to situations wherein a number of fibers that areidentical in terms of material content, physical dimensions, andphysical properties are introduced into the matrix material. Exemplaryfiber bodies of the invention are substantially free of surface stressfractures and substantially non-fibrillatable when mechanically agitatedwithin the matrix material to be reinforced, and they have a generallyquadrilateral cross-sectional profile along said elongated length,wherein average width is 1.0-5.0 mm. and more preferably 1.3-2.5 mm,average thickness is 0.1-0.3 mm and more preferably 0.05-0.25 mm., andaverage length is 20-100 mm. In preferred embodiments, average fiberwidth should exceed average fiber thickness by at least 5:1 but by nomore than 50:1, and more preferably the width to thickness ratio (forfibers having average length of 20-100 mm) is 5-20 (5:1 to 20:1).

[0064] In further exemplary embodiments of the invention, a firstplurality of individual fibers can be mixed with a second plurality ofindividual fiber bodies (i.e. comprising different materials, differentphysical dimensions, and/or different physical properties in comparisonwith the first plurality of fibers) to modify the matrix composition.The use of additional pluralities of fibers, having differentproperties, is known in the art. Hybrid blends of fibers is disclosed,for example, in U.S. Pat. No. 6,071,613 of Rieder and Berke, and thisuse of hybrid blending may be used in association with the fibers of thepresent invention as well. For example, a first plurality of fibers maycomprise polymeric material having geometry, dimensions, minimum loadcarrying capacity, and bendability as taught by the present invention,whereas a second plurality of fibers may comprise another material suchas steel, glass, carbon, or composite material. As another example, afirst plurality of fibers may have a particular bendabilitycharacteristic and/or physical dimension (in terms of average width,thickness, or length), while a second plurality of fibers may compriseidentical or similar polymer materials and employ a differentbendability characteristic and/or physical dimension(s).

[0065] Exemplary pluralities of fibers as contemplated by the presentinvention may be provided in a form whereby they are packaged orconnected together (such as by using a bag, peripheral wrap, a coating,adhesive, or such as by partial cutting or scoring of a polymerprecursor sheet, etc.). However, as previously discussed above,“individual fiber bodies” of the invention are defined as beingthemselves separated from other fiber bodies or as being separable fromother fibers when mixed into the concrete. Thus, exemplary fibers of theinvention can be said to comprise a plurality of individual fiber bodieswherein the individual fiber bodies are separated from each other orwherein individual fiber bodies are connected or partially connected toeach other but capable of becoming separated after being introduced intoand mixed within the matrix composition (to the point of substantiallyuniform dispersion).

[0066] The present inventors believe that the bendability of individualpolymer fibers can be controlled more precisely, in part, by using thegenerally quadrilateral cross-sectional profile. The present inventorssought to avoid too much flexibility whereby fibers became wrappedaround other fibers (or around themselves) such that fiber ballingarises. They also sought to avoid extreme rigidity, which is oftenassociated with strength, because this too can lead to undesirable fiber“balling.” Flexibility that is too high (such as in wet human hair) canbe just as troublesome as stiffness (such as in the “pick-up-sticks”game played by children) because self-entanglement can arise in eithercase. A high degree of fiber balling or entanglement means thatsubstantially uniform dispersion has not been attained in the matrixmaterial; and this, in turn, means that the fiber dosage will beinadequate and the material properties of the fiber reinforced materialwill be subject to significant variation.

[0067] The present inventors believe that for best dispersionproperties, bendability needs to be sufficiently high to minimize stresstransfer among the other fibers. In order to achieve this, the inventorsbelieved that alterations in the shape and size of the fiber and elasticmodulus of fibers were worth consideration. For example, a lower elasticmodulus will increase the bendability of the fiber, if the shape andsize of its cross-section remain constant. On the other hand, inventorsalso believe it is necessary to consider the elastic modulus of thematrix material to be reinforced. For polypropylene fibers, the elasticmodulus is in the range of 2-10 Giga Pascals; and for a matrix materialsuch as concrete (when hardened) the elastic modulus is in the range of20 to 30 Giga Pascals, depending on the mix design used. The presentinventors believe that to improve the properties of the matrix material(hardened concrete) especially at small crack openings or deflections,the elastic modulus of the fiber should preferably be at least as highas the elastic modulus of the matrix material (hardened concrete). Asmentioned above, an increase in elastic modulus usually means a decreasein bendability, which has a negative impact on dispersion properties ofthe plurality of fibers. Thus, in order to keep the bendability high,the present inventors have chosen to modify the both the shape andcross-sectional area of the individual fiber bodies. Fracture tests ofconcrete specimens containing the fibers have indicated that a minimumload-carrying capacity under tension (and not minimum tensile stress) offibers is needed for transferring significant stresses across a crackedsection of concrete. This also helps to keep the number of fibers perunit volume of concrete down, and this lowered dosage requirement has apositive effect in terms of improving workability of the fresh fiberreinforced concrete. It is a well-known fact that micro-fibers (havingdiameters of 20-60 micrometers) which are added to concrete for plasticshrinkage cracking control (rather than structural reinforcement, forexample) can not be added in large volumes due to the high number offibers per unit weight (e.g., high surface area). Typical dosage ratesfor these fibers range from 0.3 kg/m3 to 1.8 kg/m3 (0.033 vol. % to 0.2vol. %). Fibers added at these low dosage rates do not have asignificant effect on the hardened properties of concrete. Fibers thatare supposed to have an effect on the hardened properties of concreteneed to be added in larger volumes due to the significant higherstresses needed to be transferred across cracked concrete sections.

[0068] Ideally, the present inventors believe that fibers, used in aconcrete structure that is cracked, provide a balance between anchoringin concrete and pull-out from concrete. In other words, about half ofthe fibers spanning across the crack should operate to pull out of theconcrete while the other half of the fibers spanning the crack shouldbreak entirely, at the point at which the concrete structure becomespulled completely apart at the crack. Thus, exemplary fibers of thepresent invention are designed with particular physical dimensions thatcombine dispersibility with toughness for the purpose at hand.

[0069] An exemplary process for manufacturing fibers of the inventioncomprises: melt extruding a synthetic polymeric material (e.g.,polypropylene, polypropylene-polyethylene blend) through a dye to form asheet; cooling the extruded polymer sheet (such as by using a chilltake-up roll, passing the sheet through a cooling bath, and/or using acooling fan); cutting the sheet to provide separate individual fibers(such as by pulling the sheet through metal blades or rotary knives),whereby a generally quadrilateral cross-sectional profile is obtained(preferably having the average width and thickness dimensions asdescribed in greater detail above); stretching the polymer in thelongitudinal direction of the fibers by a factor of at least 10 to 20and more preferably by a factor of 12-16. After the stretching andcutting steps, the individual fibers can be cut to form individualbodies having average 20-100 mm lengths. Thus, exemplary individualfiber bodies of the invention will have elongated bodies, comprising oneor more synthetic polymers, having an orientation (stretch ratio) in thedirection of the length of the fiber bodies (a longitudinal orientation)of at least 10-20 and more preferably 12-16.

[0070] A further exemplary method for making the fibers with generallyquadrilateral cross-sections comprises extruding the polymer orpolymeric material through a four-cornered, star-shaped die orifice,stretching the extruded fibers by a factor of 10-20 (and more preferablyby a factor of 12-16), and cutting the stretched fibers to 20-100 mmlengths. In still further exemplary embodiments, fibers having round orelliptical shapes may be extruded, and, while still at a hightemperature, be introduced between rollers (which optionally be heated)to flatten the fibers into a generally quadrilateral shape (although inthis case the smaller faces of the fibers may have a slightly arched orconvex shape).

[0071] In addition to the fiber body embodiments mentioned above, stillfurther exemplary fiber embodiments are possible. For example,individual fiber bodies may have a variability of thickness and/or widthalong individual fiber body length of at least 2.5 percent deviation(and more preferably at least 5.0 percent deviation) and preferably nomore than 25 percent deviation from the average (thickness and/orwidth). For example, it may be possible during cutting of the polymersheet that the blades can be moved back and forth so that the width ofthe fibers can be varied within the 20-100 mm length of the individualfiber bodies.

[0072] In further exemplary embodiments, individual fiber bodies maycomprise at least two synthetic polymers, one of said at least twosynthetic polymers comprising an alkaline soluble polymer disposed onthe outward fiber surface thereby being operative to dissolve when saidfiber bodies are mixed into the alkaline environment of a wet concretemix. Alternatively, individual fiber bodies may be coated with analkaline soluble polymer. When dissolved in the alkaline environment ofa wet concrete mix, the outer surface of the fiber could be increasedfor improved keying with the concrete when hardened. An alkaline soluble(high pH) polymer material suitable for use in the present inventioncould comprise, for example, polymers of unsaturated carboxylic acids.

[0073] Exemplary fibers of the invention may also be packaged with oneor more admixtures as may be known in the concrete art. Exemplaryadmixtures include superplastizicers, water reducers, air entrainers,air detrainers, corrosion inhibitors, set accelerators, set retarders,shrinkage reducing admixtures, fly ash, silica fume, pigments, or amixture thereof. The one or more admixtures may be selected, forexample, from U.S. Pat. No. 5,203,692 of Valle et al., incorporated byreference herein. The fibers may also be coated with wetting agents orother coating materials as may be known to those of ordinary skill inthe concrete industry.

[0074] Further features and advantages of the exemplary fibers, matrixcompositions, and processes of the invention may be illustrated byreference to the following examples.

EXAMPLE 1 Prior Art

[0075] Prior art fibers having an elliptical shaped cross section weretested in terms of bendability and dispersibility in a concrete mix.These elliptical fibers were 50 mm long, 1.14 mm wide, 0.44 mm. thick,and had a Young's modulus of elasticity of 4 Giga Pascal. The“bendability” formula discussed above may be employed, whereinbendability “B” was computed as B=1/(3·E·I), and the moment of inertia“I” for ellipses is calculated by the formula, I_(ellipse)=Pi/64·a·b³,where “a” is half the width of the elliptical fiber (major axis of theellipse, i.e., widest dimension through the center) and “b” is half thethickness of the elliptical fiber (minor axis of the ellipse, i.e.thinnest dimension through the center point of the ellipse). The bendingdeflection “B” was computed to be 17.5 mN⁻¹*m⁻². This fiber isconsidered a “stiff” fiber. 30 minutes were required for introducing 100pounds of these elliptical fibers into 8 cubic yards of concrete. Theconcrete resided in the drum of a ready-mix truck and was rotated at 15revolutions per minute (rpm). Excessive fiber balling was observed. Theelliptical fibers did not disperse in this concrete.

EXAMPLE 2

[0076] In contrast to the prior art elliptical fibers of Example 1,fibers having a generally quadrilateral cross-section were used. Thesequadrilateral fibers had the following average dimensions: 50 mm long,1.35 mm wide, and 0.2 mm thickness, with a Young's modulus of elasticityof 9 Giga Pascal. The bendability “B” of these fibers was computed inaccordance with the formula, B=1/(3·E·I), wherein the moment of inertia“I” for rectangular cross-section was computed in accordance with theformula, I_(rectangle)={fraction (1/12)}·w·t³, wherein “w” is theaverage width and “t” is the average thickness of the rectangle. Usingthe equation, the bendability “B” was computed as 41.2 mN⁻¹*m⁻². Thisfiber is considered flexible. When 100 pounds of these fibers wereintroduced into 8 cubic yards of concrete, located in a ready-mix truckdrum and rotated at the same rate as in Example 1, a homogeneous fiberdistribution was achieved in just 5 minutes. No fiber balling wasobserved.

EXAMPLE 3

[0077] The mechanical properties of the fibers themselves have a hugeimpact on the behavior of the fibers in concrete, if there is sufficientbond between the fiber and the brittle concrete matrix. If the fibershave not bonded well to the matrix (e.g. fiber pull-out is the majorfiber failure mechanism observed when the fiber reinforced concrete isbroken apart), then the fiber properties will have minimal impact on thebehavior of the composite material. As mentioned earlier, due to thefiber geometry and dimensional ranges inventively selected by thepresent inventors, sufficient bond adhesion between the matrix material(when hardened) and the fibers can be achieved to obtain, ideally, halffiber failure (breakage) and half fiber pull-out. Therefore, fiberproperties such as elastic modulus of elasticity, tensile strength, andminimum load carrying capacity were selected so as to maintain asclosely as possible the ideal 50:50 balance between fiber pull-outfailure and fiber failure. The optimum mechanical properties of thefibers will highly depend on the strength of the matrix: a higherstrength matrix will require a fiber with a higher elastic modulus,higher tensile strength, and higher minimum load carrying capacity.

[0078] All the mechanical tests performed on the fiber itself have to bedone in direct tension (i.e., longitudinal direction), which is also themode the fibers fail when embedded in hardened concrete. (Commerciallyavailable machines for such testing are available from known sourcessuch as Instron or Material Testing Systems). For these mechanicaltests, a fiber filament, usually 100 mm long, is fixed on both ends withspecial fiber yarn grips that do not allow the fiber to slip. The fiberis slightly pre-stretched (less than 2 Newton of load is measured). Aload cell measures the tensile load while the fiber is being pulledapart at a constant rate. Typical rates of loading range from 25 mm/min.to 60 mm/min. The strain is measured using an extensometer, which isclamped onto the sample. Strain is defined as the length change dividedby the initial length (also called gauge length) multiplied by 100 andis recorded in terms of percentage. The initial gauge for themeasurements was set to 50 mm.

[0079]FIG. 13 shows various load versus strain curves of fibers withdifferent cross sectional areas. Fibers with number 1 are thinner thanfibers with the number 2. The letters “A”, “B”, “C” are related to thewidth of the fibers: “A” is the fiber with the smallest width, while “C”is the fiber with the largest width. Therefore, the fiber with thesmallest cross sectional area is fiber “1A”, while the fiber with thelargest cross section is fiber “2C”.

[0080] These curves provided in this example show that a fiber with asmall cross sectional area has a much lower minimum load carryingcapacity than a fiber with a larger cross sectional area. Individualfiber bodies should have a minimum load carrying capacity such that aplurality of the fibers will cumulatively provide a total load-carryingcapacity exceeding the tensile stress at which the concrete matrixmaterial failed (i.e. the typical stress at failure for the concretematrix is somewhere in the range of 2 to 5 Mega Pascals). The inventorsbelieve that a minimum load carrying capacity (in tension) of the fiberis necessary in order to transfer stresses effectively as well askeeping the number of individual fibers down. By keeping the fibernumbers down, the workability of the fresh concrete can be maintained.

EXAMPLE 4

[0081]FIG. 14 shows the tensile stress versus strain curves of thefibers described in the previous example. “Stress” is defined as theload divided by the cross sectional area of the fiber. The slope of theinitial part of the ascending curve is directly proportional to themodulus of elasticity of the fiber material. As mentioned earlier, themodulus of elasticity of the fiber should preferably be as close aspossible to the modulus of elasticity of the matrix material, so as totransfer tensile loads across cracks in the matrix immediately afterthey have been initiated. On the other hand, a higher elastic modulusdecreases bendability (i.e. increases stiffness) of the fibers; theinventors discovered that this diminishes the dispersibility of fibersin wet concrete. To minimize the adverse effect of a high elasticmodulus on the bendability of the fiber, the inventors selected agenerally quadrilateral cross-sectional profile and selected a thinnerand wider fiber.

[0082] The stress-versus-strain curves shown in FIG. 14 indicate thatthe elastic moduli and tensile strengths of the different fiber samplesare approximately the same (up to around 7% strain). However, as shownin FIG. 16, the use of different cross-sectional dimensions had aprofound effect on the performance of the different fiber samples in theconcrete.

EXAMPLE 5

[0083] The effect of different geometries of the fibers, as well asdifferent minimum load carrying capacities on the mechanical propertiesof fiber reinforced concrete, can be studied using fracture tests. Thebasic principle of a fracture test performed on a given material is tosubject a specimen (in this case the fiber reinforced concrete) to aload that initiates cracking in a controlled manner, while measuring theapplied load and the deformation and eventual crack opening of thespecimen. A suitable test for concrete is the Wedge Splitting Test,which is based on a modified Compact-Tension specimen geometry. The testset-up is described in the Austrian Patent AT 390,328 B (1986) as wellas in the Austrian Patent AT 396,997 B (1996).

[0084]FIG. 15 depicts a typical uniaxial wedge splitting test devicethat can be used for measuring load on concrete materials. A notchedcube-shaped concrete specimen resting on a linear support (which is muchlike a dull knife blade is split) with load transmission equipmentsituated in a rectangular groove extending vertically down into the topof the sample concrete specimen. The load transmission equipmentconsists of a slim wedge (a) and two load transmission pieces (b) withintegrated needle bearings. The crack mouth opening displacement (CMOD)is measured by two electronic displacement transducers (Linear VariableDifferential Transducer or “LVDT” gauges) located on opposing sides ofthe crack. Both LVDTs (d) are mounted in a relatively simple way on aCMOD measurement device (c) that is attached to the specimen with screwbolts.

[0085] The crack initiates at the bottom of the starter notch andpropagates in a stable manner from the starter notch on top of theconcrete sample to the linear support below the sample. To obtain aload-versus-displacement curve, the two crack mouth opening displacementsensors, CMOD1 and CMOD2, and the applied load (downward through thewedge), are recorded simultaneously.

[0086] To maintain an approximately constant rate of crack opening, thetest is performed with a rigid testing machine at a constant cross-headspeed of 0.5 mm/min. to 1.0 mm/min. depending on the wedge angle. Theapplied machine load, FM, the vertical displacement, δv, and the crackmouth opening displacement, CMOD, are recorded simultaneously at leastevery second. The fracture energy, G_(F), a measure of the energyrequired to widen a crack, is determined from a load-displacement curveby using the formula$G_{F} = {\frac{1}{B \cdot W} \cdot {\int_{0}^{{CMOD}_{\max}}{{F_{H}({CMOD})} \cdot {({CMOD})}}}}$${\text{with}\quad {CMOD}} = {\frac{1}{2}\left( {{CMOD1} + {CMOD2}} \right)}$

[0087] where “B” is the ligament height, “W” is the ligament width (Btimes W is the crack surface area), and “FH” is the horizontal splittingload which may be calculated using the following equation,$F_{H} = \frac{F_{M} + {m_{W} \cdot 9.81}}{2 \cdot {\tan \left( {\alpha/2} \right)}}$

[0088] wherein “F_(M)” is the applied machine load, “m_(w)” is the massof the splitting wedge, and “Δ” is the wedge angle.

[0089] As a measure for the energy for crack initiation, the criticalenergy release rate “G_(Ic)” is calculated (plane stress assumed):$G_{Ic} = {{\frac{K_{Ic}^{2}}{E}\quad \text{with}\quad K_{Ic}} = {k \cdot F_{H,\max}}}$

[0090] where “K_(Ic)” is the critical stress intensity factor, which isproportional to the maximum splitting load “F_(H, max)” The constant kdepends on the specimen geometry and can be calculated by a finiteelement program.

[0091] The stress factor “KI” is defined as following:

K _(I) =k·F _(H)

[0092] where “F_(H)” is the horizontal load measured during the fractureof the specimen. The stress factor is independent of the specimen size,which can be used to compare the behavior of different specimens andmaterials.

[0093] The effect of the fiber on the mechanical properties of thecomposite material can be seen after a crack is initiated. FIG. 16 showsthe stress-versus-crack opening behavior of different fiber geometriesand fiber materials. The larger the area under the curve, the moreenergy the composite material can absorb while it is being broken apart.This phenomenon is also called ‘toughening’ of a material. The higherthe ‘toughness’ of a material with a certain fiber dosage (volume %),the higher is the resistance to crack propagation of the material. If acertain fiber achieves similar toughness at a lower dosage, as comparedto other fibers, then such a fiber will be considered to be a moreeffective reinforcing fiber.

[0094]FIG. 16 shows that flat, substantially non-fibrillatable fibers ofthe present invention are much more effective when compared to theperformance of fibrillatable fibers of similar dimensions (wheninitially introduced into the concrete) and similar dosage. FIG. 16 alsodemonstrates that the performance of a flat PVA fiber (used at 25%higher dosage rate) with respect to resisting propagation at small crackopenings is slightly better than that of other fibers. However, atlarger crack openings, the exemplary flat fibers of the presentinvention clearly outperformed the flat PVA fiber in resisting higherdeformations.

[0095] Further exemplary embodiments of the invention provide syntheticfibers, and matrix materials comprising such fibers, that areparticularly suited for retaining a smooth finish when embedded inmatrix materials such as concrete. In this respect, the inventorsbelieve that the bendability of the fibers is an important key forobtaining finishability. Fibers that are not flexible enough tend to popup again after the concrete finisher has attempted to smooth out(finish) the concrete surface.

[0096] The inventors believe that finishability is a function of thebendability and the length of the fiber. To achieve the same kind offinishability (wherein fibers do not pop out of a smoothed concretesurface), longer fibers need to be more flexible (i.e., they must have ahigher bendability) than shorter fibers.

[0097] For example, a fiber that is 40 mm long, 0.105 mm thick, and 1.4mm wide (with a Young's modulus of 9.5 GPa) can be observed to have gooddispersion properties and excellent finishibality characteristics.Fibers having a length of 40 mm, a thickness of 0.14 mm, and a width of1.4 mm (with a Young's modulus of 9.5 GPa) showed acceptable dispersionproperties (e.g., a few fiber balls per truck when added in the same wayas the previous more bendable fiber), but it did not finish as well asthe above mentioned fiber. When similar fibers, having length of 50 mm,are added to a concrete ready-mix truck, more fibers sticking out of thesurfacecan be seen despite having the same bendability.

[0098] It was thus discovered by the present inventors that exemplaryfibers as just described can have excellent toughness properties atdifferent compressive strength levels. For example, with 0.5% or 4.6kg/m3 of fibers, a R_(e,3) value of more than 50% can be achieved withconcrete compressive strength range between 10 and 35 MPa which issuitable for flooring (measured according to ASTM C 1018 (1997) orJCI-SF 4 on a 150 by 150 by 500 mm³ beam). Incidently, the R_(e,3) valuerepresents the ductility factor of a fiber-reinforced concrete sample(e.g., beam), and this may be calculated as a ratio of the equivalentflexural strength (measured after first cracking and at a deflection of3 mm, wherein the fibers are bridging the crack) divided by the originalflexural strength of the beam (first cracking strength). See ASTM C 1018(1997)). The R_(e,3) value was found, for a given dosage of fibers,depended on the strength of the concrete matrix, particularly higherstrength concrete (e.g., in the range above 35 MPa). The fibercross-section was then increased such that the tensile resistance wasincreased while appropriate bendability for good finishability anddispersion was maintained. The inventors achieved this by increasingwidth and reducing thickness. The length of the fiber was also adjustedto maximize the R_(e,3) value.

[0099] The inventors also discovered that in dry-mix shotcrete a morebendable fiber had a lower rebound value compared to a less bendablefiber. In other words, the impact of the sprayed material did not bounceoff (i.e., rebound from) the surface being sprayed.

[0100] Moreover, the inventors believe that the length and bendabilityof fibers greatly affect the finishability of concrete flooring. Longerfibers with the same bendabilty index did not have a finishability equalto the shorter fibers (i.e., they tended to pop up more from theconcrete surface after it was smoothed). The amount of fiber “pop up” isbelieved to be directly related to the amount of elastic energy storedin the fiber which is being pushed below or into the surface of theconcrete by the smoothing motion of the person who is doing thefinishing. The higher the energy needed for pushing fibers into theconcrete surface, the more likely the fibers will pop up again. Inconsidering this relationship, the inventors realized that the storedelastic energy depends partly upon the level of bending restraintbestowed upon the fiber by portions embedded in the concrete material,partly upon the exposed length of the fibers sticking out from thesurface of the concrete surface, and partly upon the bendability of thefibers.

[0101] Hence, the inventors surmise that longer fibers will, on average,tend to have greater portions of their length embedded in the concretemass, thereby providing more restraint at the point of bending. Thisgreater restraint will tend to increase the elastic energy stored in thefiber during the finishing process; and this, in turn, will tend toincrease the incidence of fiber pop-up from the finished surface.However, in the case of shorter fibers having the same bendability, theembedded length is likely to be shorter on average, and, hence, lessrestraint would be imposed at the point of bending. Therefore, the loweramount of elastic energy stored in shorter fibers make them less likelyto cause fiber pop-up at the concrete surface. In another words, shorterfibers tend to pull out and move with the trowel or othersurface-finishing device more easily at a concrete surface that is beingsubjected to concrete finishing, and this is believed to be due to thelower restraint of the shorter fibers causing the fiber to lay down withless elastic bending energy stored in the fiber.

[0102] Therefore, to achieve similar finishability, a longer fiber willneed to have greater bendability to minimize the elastic energy storedin the fiber, which otherwise will tend to force fibers to stick out ofthe finished concrete surface.

[0103] The modulus of elasticity, also called Young's Modulus, is theconstant relating stress and strain for a linearly elastic material. Inpractical terms, modulus of elasticity is a measure of a material'sstiffness. The higher the modulus of elasticity, the stiffer a materialis. Modulus of elasticity is determined by chemical composition. Modulusof elasticity may be expressed in terms of pounds per square inch (1b/in²) also in terms of MegaPascals (MPa). One (1) MPa is equal to one(1) Newton/mm².

[0104] As shown in FIG. 17, a typical stress-strain curve can be used toillustrate physical properties of a material. The number (1) shown inFIG. 17 indicates the slope of the stress-strain curve corresponding tothe elastic nature of the material, and this is referred to as themodulus of elasticity. By definition, the proportional limit which isindicated in FIG. 17 by the number (2) represents the first point atwhich the elastic behavior of the stress-strain curve is non-linear.This point can also be thought of as the limit of elasticity, for beyondthis point the specimen will begin to demonstrate permanent deformationafter removal of the load, due to plastic strain.

[0105] The moment of inertia describes the property of matter to resistany change in rotation. The moment of inertia, I, for an area of aparticular shape (e.g., rectangle, ellipse or circle) may be calculatedusing the appropriate formula:$I_{rectangle} = {\frac{1}{12} \cdot w \cdot t^{3}}$$I_{ellipse} = {\frac{\pi}{64} \cdot a \cdot b^{3}}$$I_{circle} = {\frac{\pi}{64} \cdot D^{4}}$

[0106] where “w” represents the length, “t” represents the breadth (ofrectangle), “a” represents the major axis and “b” the minor axis of anellipse, and “D” represents the diameter of a circle.

[0107] Bendability of a fiber can be defined as the resistance of thefiber to change its shape when an external load is applied. A fiber willbe termed more bendable if it requires less force to bend it to acertain degree. The bending flexibility of a fiber is a function ofshape, cross-sectional size, and modulus of elasticity. The bendability,B, of a fiber can be calculated using the formula:$B = \frac{1}{3 \cdot E \cdot I}$

[0108] Using the above equation, the bendability, B, of a 1.2 mm wideand 0.38 mm thick fiber with an elliptical shaped cross section with anelastic modulus of 4 GPa is 26.2 mN⁻¹*m⁻². This fiber is considered astiff fiber. When these fibers were added to the concrete in a ready-mixtruck (100 pounds of fibers were added to a 8 cubic yard concrete loadin 30 minutes, while the drum was rotating with 15 rpm), excessive“fiber-balling” was observed and very poor finishibality was observed:The fibers did not disperse in the concrete, but bundles of fibersstayed together.

[0109] Another example involves 50 mm long flat fibers that were 1.4 mmwide and 0.2 mm thick with an elastic modulus of 9 GPa. The bendability,B, is 39.7 mN⁻¹*m⁻², using the above equation. This fiber is considereda more flexible fiber. When these fibers were added to the concrete inthe same manner as in the above-described example with the stiff fiberbut in just 5 minutes, a few fiber balls were observed. A homogeneousfiber distribution throughout the concrete mix was achieved due to themore flexible nature of the fiber. The finishibility improved comparedto the previous example, but still not satisfactory for allapplications.

[0110] Another example involves 40 mm long flat fibers that were 1.4 mmwide and 0.105 mm thick with an elastic modulus of 9.5 GPa. Thebendability, B, is 259.8 mN⁻¹*m⁻², using the above equation. This fiberis considered a highly flexible fiber. When these fibers were added tothe concrete in the same manner as in the above-described example alsoin just 5 minutes, no fiber balls were observed. A homogeneous fiberdistribution throughout the concrete mix was achieved due to the highlyflexible nature of the fiber. Excellent finishibility was consistentlyachieved with this fiber.

[0111] When the finishability of the fiber A with a bendability of 39.7mN⁻¹*m⁻² was compared to the finishability of a fiber B with abendability of 259.8 mN⁻¹*m⁻², the following observations were made.After the concrete was finished, fiber A tended to pop out of theconcrete surface after the power trowel had pushed them down (theconcrete appeared to have “goose bumps”). On the other hand, when thesame finish was applied to a concrete containing fiber B, the fibersstayed within the concrete surface. The elastic energy stored in thefibers was too small to cause them to pop out of the surface. After thepower trowel finish, nearly no fibers were visible at the concretesurface when the concrete slab was inspected a day later.

[0112] For a fiber with optimized dispersion properties, the bendabilityhas to be high enough to minimize stress transfer among fibers. In orderto achieve this, the shape and the size or elastic modulus of the fibercan be changed. A lower elastic modulus increases the bendability of thefiber, if the shape and the size of the cross section remain unchanged.For polypropylene fibers the elastic modulus is in the range of 3 to 20GPa (for comparison concrete has an elastic modulus of 20 to 30 GPadepending on the mix design used). To improve the hardened properties interms of toughness of fiber reinforced concrete, especially at smallcrack openings (up to 1 mm), the elastic modulus of the fiber preferablyshould be at least as high as or higher than the elastic modulus of thematrix (concrete). As discussed above, a higher elastic modulusdecreases bendability, which has a negative impact on the dispersionproperties of the fibers. To maintain high bendability, the fiber shapeand the cross sectional area have to be changed. Fracture tests showedthat a minimum load carrying capacity under tension (NOT minimum tensilestress) of fibers is required in order to be able to transfersignificant stresses across a cracked section of concrete. This alsohelps to keep the number of fibers per volume percent down, which has apositive effect on the workability of fresh fiber reinforced concrete.It is a well-known fact that microfibers (having diameters of 20 to 60micrometer), added primarily to minimize cracking due to plasticshrinkage in concrete, cannot normally be added in large volumes, onaccount of the high numbers per unit weight ratio. Typical dosage ratesrange from 0.3 kg/m³ to 1.8 kg/m³ (0.03 vol. % to 0.2 vol. %), such thatthe fibers do not significantly affect the properties of the hardenedconcrete. Fibers intended to affect (i.e., reinforce) hardened concretenormally require higher addition volumes to transfer significantstresses across cracks in the concrete.

[0113] Exemplary fibers of the invention which are believed to provideexcellent finishability to the surface of hydratable cementitiousmaterials comprise: a plurality of individual fiber bodies having anelongated length defined between two opposing ends and comprising atleast one synthetic polymer, the individual fiber bodies beingsubstantially free of stress fractures and substantiallynon-fibrillatable when mechanically agitated within the matrix materialto be reinforced, wherein, in said plurality of individual fiber bodies,the average bendability of said fiber bodies is 100-2,500 mN⁻¹*m⁻².Preferred high-finishability fibers also have the exemplary properties:a Young's modulus of elasticity of 4-20 Giga Pascals, tensile strengthof 400-1,600 Mega Pascals. Preferably, the individual fiber bodies aresubstantially free of stress fractures and substantiallynon-fibrillatable when mechanically agitated within the matrix materialto be reinforced, the fiber bodies having a generally quadrilateralcross-sectional profile along said elongated length, thereby havingwidth, thickness, and length dimensions, wherein average width is1.0-5.0 mm, average thickness is 0.05-0.2 mm, average length is 20-75mm; and wherein average width preferably exceeds average thickness by afactor of 5 to 50.

[0114] Exemplary high-finishability fibers of the invention comprise atleast one synthetic polymer selected from the group consisting ofpolyethylene, polypropylene, polyoxymethylene, poly(vinylidinefluoride), poly(methyl pentene), poly(ethylene-chlorotrifluoroethylene),poly(vinyl fluoride), poly(ethylene oxide), poly(ethyleneterephthalate), poly(butylene terephthalate), polyamide, polybutene, andthermotropic liquid crystal polymers.

[0115] Exemplary high-finishability fibers have individual fiber bodieswherein the average bendability is 150-2,000 mN⁻¹*m⁻². Particularlypreferred high-finishability fibers are substantially free of stressfractures and substantially non-fibrillatable when mechanically agitatedwithin the matrix material to be reinforced, and have a generallyquadrilateral cross-sectional profile along their elongated length,thereby having width, thickness, and length dimensions, wherein theaverage width is 1.0 to 3.0 mm; average thickness is 0.05 to 0.15 mm,average length is 20 to 60 mm, wherein average fiber width exceedsaverage fiber thickness by a factor of 7 to 40.

[0116] Further preferred high-finishability fibers of the inventioncomprise a plurality of individual fiber bodies having an elongatedlength defined between two opposing ends and comprising at least onesynthetic polymer, said individual fiber bodies being substantially freeof stress fractures and substantially non-fibrillatable whenmechanically agitated within the matrix material to be reinforced, thefiber bodies having a generally quadrilateral cross-sectional profilealong said elongated length, thereby having width, thickness, and lengthdimensions wherein the average width is no less than 1.0 to 3.0 mm,average thickness is 0.075 to 0.15 mm, average length is 20 to 60 mm,average fiber width to thickness ratio is 7 to 30, a Young's modulus ofelasticity of 4 to 20 Giga Pascals, a tensile strength of 400 to 1,600Mega Pascals, a minimum load carrying capacity in tension mode of 20 to1,000 Newtons per fiber body, the fiber bodies preferably also having anaverage square area to volume ratio of 10.5 to 42 mm⁻¹; and alsopreferably having an average bendability of 150 to 2,500 mN⁻¹*m⁻².

[0117] The present invention also provides matrix compositionscomprising the above-described fibers. An exemplary matrix compositionmay be comprised of an adhesive, asphalt, composite material, plastic,elastomer, hydratable cementitious materials, or mixtures thereof.Preferred matrix compositions are hydratable cementitious composition(e.g., concrete, wet-mix and dry-mix shotcrete, dry mortar, mortar,cement paste), and preferred fibers comprise polypropylene,polyethylene, or mixture thereof. Preferably, the fibers are present inhydratable matrix compositions in amounts of 0.05% to 2.0% by volume.

[0118] The invention provides high finishability fibers as well ascementitious materials containing such fibers. When the fibers areembedded in concrete, the concrete preferably will have a compressivestrength in the range of 30 to 60 MPa wherein the average R_(e,3) valueis 20 to 60%, and the concrete will have a finishablity wherein embeddedfibers do not substantially stick out of said concrete (as visuallyconfirmed by naked eye inspection of the surface of the concrete. Theaverage bendability of the fiber bodies is preferably 100 to 2,500mN⁻¹*m⁻²; the average width is preferably 1.0 to 3.0 mm; the averagethickness is 0.075 to 0.15 mm; the average length is preferably 20 to 60mm; the fibers having a Young's modulus of elasticity of 4 to 20 GigaPascals; and the fibers having a tensile strength of 400 to 1,600.

[0119] The invention is also directed to concrete flooring, andparticularly floor slabs, containing embedded fibers as described above.Such fiber-embedded cementitious or concrete floors preferablycompressive strength of 15 to 40 MPa, an average R_(e,3) value of 20 to60%, and finishability (wherein embedded fibers do not substantiallystick out of the concrete), the fibers also having an averagebendability of 100 to 2,500 Mn⁻¹*m⁻², an average width of 1.0 to 4.0 mm,an average thickness of 0.050 to 0.15 mm, an average length of 20 to 60mm, a Young's modulus of elasticity of 4 to 20 Giga Pascals; andpreferably a tensile strength of 400 to 1,600 Mega Pascals.

[0120] Still further exemplary fibers have a twist shape, for example asa result of being cut into separate pieces from strands twisted in themanner of a rope or cable.

[0121] The present invention is not to be limited by the foregoingexamples and illustrations which are provided for illustrative purposesonly.

It is claimed:
 1. Fibers for reinforcing matrix materials, comprising: aplurality of individual fiber bodies having an elongated length definedbetween two opposing ends and comprising at least one synthetic polymer,said individual fiber bodies being substantially free of stressfractures and substantially non-fibrillatable when mechanically agitatedwithin the matrix material to be reinforced, said fiber bodies having agenerally quadrilateral cross-sectional profile along said elongatedlength, thereby having width, thickness, and length dimensions, whereinthe average width is at least 1.0 mm; wherein the average width is nomore than 5.0 mm; wherein the average thickness is at least 0.1 mm;wherein the average thickness is no more than 0.3 mm; wherein theaverage length is at least 20 mm; and wherein the average length is nomore than 100 mm.
 2. The fibers of claim 1 wherein said average width isno less than 1.3 mm; said average width is no greater than 2.5 mm; saidaverage thickness is no less than 0.15 mm; said average thickness is nogreater than 0.25 mm; said average length is no less than 30 mm; andsaid average length is no greater than 60 mm.
 3. The fibers of claim 1wherein, in said plurality of individual fiber bodies, said individualfiber bodies are separated from each other.
 4. The fibers of claim 1wherein, in said plurality of individual fiber bodies, said individualfiber bodies are partially separated from each other but are completelyseparable when mechanically agitated within the matrix material.
 5. Thefibers of claim 1 wherein, in said plurality of individual fiber bodies,said at least one synthetic polymer is selected from the groupconsisting of polyethylene, polypropylene, polyoxymethylene,poly(vinylidene fluoride), poly(methyl pentene),poly(ethylene-chlorotrifluoroethylene), poly(vinyl fluoride),poly(ethylene oxide), poly(ethylene terephthalate), poly(butyleneterephthalate), polyamide, polybutene, and thermotropic liquid crystalpolymers.
 6. The fibers of claim 1 wherein said fiber bodies comprisepolypropylene in an amount no less than 75% by weight and said fiberbodies comprise polypropylene in an amount up to 100%.
 7. The fibers ofclaim 6 wherein said fiber bodies comprise a blend of at least twopolymers or a co-polymer comprising at least two of said polymers. 8.The fibers of claim 7 wherein said fiber bodies comprise polypropyleneand polyethylene.
 9. The fibers of claim 1 wherein said fiber bodieshave a Young's modulus of elasticity of no less than 3 Giga Pascals andwherein said fiber bodies have a Young's modulus of elasticity no morethan 20 Giga Pascals.
 10. The fibers of claim 1 wherein said fiberbodies have a tensile strength of no less than 350 Mega Pascals andwherein said fiber bodies have a tensile strength of no more than 1200Mega Pascals.
 11. The fibers of claim 1 wherein said fiber bodies have aminimum load carrying capacity in tension mode of no less than 40Newtons per fiber body and said fiber bodies have a minimum loadcarrying capacity in tension mode of no more than 900 Newtons per fiberbody.
 12. The fibers of claim 1 wherein said fiber bodies have a widthto thickness ratio of no less than 4 and wherein said fiber bodies havea width to thickness ratio of no more than
 50. 13. The fibers of claim 1wherein said fiber bodies have a width to thickness ratio of no lessthan 5 and wherein said fiber bodies have a width to thickness ratio ofno more than
 20. 14. The fibers of claim 1 wherein said fiber bodieshave an average bendability “B” of no less than 20 mN⁻¹*m⁻² and whereinsaid fiber bodies have an average bendability “B” of no more than 1300mN⁻¹*m⁻², said bendability “B” of said fibers being determined inaccordance with the formula, B=1/(3·E·I), wherein the moment of inertia“I” for a generally rectangular cross-section is computed in accordancewith the formula, I_(rectangle)={fraction (1/12)}·w·t³, wherein “w” isthe average width and “t” is the average thickness of the generallyrectangular cross-section.
 15. The fibers of claim 1 wherein said fiberbodies have an average bendability “B” of no less than 25 mN⁻¹*m⁻² andwherein said fiber bodies have an average bendability “B” of no morethan 500 mN⁻¹*m⁻², said bendability “B” of said fibers being determinedin accordance with the formula, B=1/(3·E·I), wherein the moment ofinertia “I” for a generally rectangular cross-section is computed inaccordance with the formula, I_(rectangle)={fraction (1/12)}·w·t³,wherein “w” is the average width and “t” is the average thickness of thegenerally rectangular cross-section.
 16. The fibers of claim 1 whereinsaid fiber bodies have an average surface square area “S_(A)” to volume“V” ratio of no less than 7.0 mm⁻¹ and wherein said fiber bodies have anaverage S_(A) to V ratio of no more than 22.1 mm⁻¹.
 17. The fibers ofclaim 16 wherein said fiber bodies have an average surface square area“S_(A)” to volume “V” ratio of no less than 10 mm⁻¹ and wherein saidfiber bodies have an average S_(A) to V ratio of no more than 15 mm⁻¹.18. The fibers of claim 1 further comprising a second plurality ofindividual fiber bodies, wherein said second plurality differs in termsof fiber composition, dimensions, a physical characteristic, orcombination thereof.
 19. The fibers of claim 1 being coated, bundled,packaged, packeted, coated, adhered, or contained together.
 20. Thefibers of claim 19 wherein said individual fiber bodies are partiallyconnected together as a scored sheet which is operative to separate intosaid individual fiber bodies when said sheet is introduced into, andmechanically agitated, in a hydratable cementitious composition.
 21. Thefibers of claim 1, wherein said matrix materials are hydratablecementitious compositions.
 22. Fibers for reinforcing matrix materials,comprising: a plurality of individual fiber bodies having an elongatedlength defined between two opposing ends and comprising at least onesynthetic polymer, said individual fiber bodies being substantially freeof stress fractures and substantially non-fibrillatable whenmechanically agitated within the matrix material to be reinforced, saidfiber bodies having a generally quadrilateral cross-sectional profilealong said elongated length, thereby having width, thickness, and lengthdimensions wherein the average width is no less than 1.0 mm; wherein theaverage width is no more than 5.0 mm; wherein the average thickness isno less than 0.1 mm; wherein the average thickness is no more than 0.3mm; wherein the average length is no less than 20 mm; wherein theaverage length is no more than 100 mm; wherein the average fiber widthto thickness ratio is no less than 5; wherein the average fiber width tothickness ratio is no more than 50; wherein said fiber bodies have aYoung's modulus of elasticity no less than 3 Giga Pascals; wherein saidfiber bodies have a Young's modulus of elasticity no more than 20 GigaPascals; wherein said fiber bodies have a tensile strength no less than350 Mega Pascals; wherein said fiber bodies have a tensile strength ofno more than 1200 Mega Pascals; wherein said fiber bodies have a minimumload carrying capacity in tension mode no less than 40 Newtons per fiberbody; wherein said fiber bodies have a minimum load carrying capacity intension mode no greater than 900 Newtons per fiber body; wherein saidfiber bodies have an average square area to volume ratio no less than7.0 mm⁻¹; wherein said fiber bodies have an average square area tovolume ratio no more than 22.1 mm⁻¹; wherein said fiber bodies have anaverage bendability “B” no less than 25 mN⁻¹*m⁻²; and wherein said fiberbodies have an average bendability “B” no more than 500 mN⁻¹*m⁻²; saidbendability “B” of said fibers being determined in accordance with theformula, B=1/(3·E·I), wherein the moment of inertia “I” for a generallyrectangular cross-section is computed in accordance with the formula,I_(rectangle)={fraction (1/12)}·w·t³, wherein “w” is the average widthand “t” is the average thickness of the generally rectangularcross-section.
 23. A matrix composition comprising said fibers of claim1 and a matrix material selected from the group consisting of adhesives,asphalt, composite materials, plastics, elastomers, and hydratablecementitious materials.
 24. The matrix composition of claim 23 whereinsaid matrix material is a hydratable cementitious composition and saidfibers comprise polypropylene.
 25. The matrix composition of claim 23wherein said fibers are present in the matrix composition in the amountno less than 0.05% by volume and wherein said fibers are present in thematrix composition in an amount no greater than 10% by volume. 26.Method for modifying a matrix material, comprising introducing into amatrix material the fibers of claim
 1. 27. Process for manufacturingfibers, comprising: melt extruding at least one synthetic polymericmaterial through a sheet dye; cooling the extruded sheet to belowambient temperature; cutting the extruded sheet to form separate fibersto achieve a generally quadrilateral cross-sectional provide andresultant average width and thickness dimensions, wherein the averagewidth is at least 1.0 mm, wherein the average width is no more than 5.0mm, wherein the average thickness is at least 0.1 mm, and wherein theaverage thickness is no more than 0.3 mm; stretching said fiberslongitudinally by a factor no less than 10 and no greater than 20; andcutting said fibers to provide average fiber length no less than 20 andno greater than 100 mm.
 28. The process of claim 27 wherein saidstretching said fiber longitudinally precedes said cutting to provideaverage fiber lengths of no less than 20 and no greater than 100 mm. 29.The process of claim 27 wherein said cutting to provide average fiberlengths of no less than 20 and no greater than 100 mm precedes saidstretching.
 30. The process of claim 27 wherein said cooling comprisestaking up said melt extruded polymeric material on a chill roll.
 31. Theprocess of claim 27 wherein said cooling comprises passing said meltextruded polymeric material through a water bath.
 32. The fibers ofclaim 1 wherein said individual fiber bodies have a variability ofthickness or width along the individual fiber body length of no lessthan 2.5 percent deviation from average thickness or width as the casemay be, and wherein said individual fiber bodies have a variability ofthickness or width along the individual fiber body length of no greaterthan 25 percent deviation from the average thickness or width as thecase may be.
 33. The fibers of claim 1 wherein said individual fiberbodies comprise at least two synthetic polymers, one of said at leasttwo synthetic polymers comprising an alkaline soluble polymer disposedon the outward fiber surface thereby being operative to dissolve whensaid fiber bodies are mixed into the alkaline environment of a wetconcrete mix.
 34. The fibers of claim 1 wherein said individual fiberbodies are coated with an alkaline soluble polymer operative to dissolvewhen said fiber bodies are mixed into the alkaline environment of a wetconcrete mix.
 35. The fibers of claim 1 wherein said plurality of fibersare contained in packaging with an admixture.
 36. The fibers of claim 35wherein said admixture is selected from the group consisting of asuperplastizicer, water reducer, air entrainer, air detrainer, corrosioninhibitor, set accelerator, set retarder, shrinkage reducing admixture,fly ash, silica fume, pigments, or a mixture thereof.
 37. Fibers forreinforcing matrix materials, comprising: a plurality of individualfiber bodies having an elongated length defined between two opposingends and comprising at least one synthetic polymer, said individualfiber bodies being substantially free of stress fractures andsubstantially non-fibrillatable when mechanically agitated within thematrix material to be reinforced, wherein, in said plurality ofindividual fiber bodies, the average bendability of said fiber bodies isno less than 100 mN⁻¹*m⁻²; and the average bendability of said fibers isno more than 2,500 mN⁻¹*m⁻².
 38. The fibers of claim 37 wherein, in saidplurality of individual fiber bodies, said fiber bodies have a Young'smodulus of elasticity of no less than 4 Giga Pascals and no more than 20Giga Pascals.
 39. The fibers of claim 37 wherein, in said plurality ofindividual fiber bodies, said fiber bodies have a tensile strength of noless than 400 Mega Pascals and no more than 1,600 Mega Pascals.
 40. Thefibers of claim 37 wherein said individual fiber bodies aresubstantially free of stress fractures and substantiallynon-fibrillatable when mechanically agitated within the matrix materialto be reinforced, said fiber bodies having a generally quadrilateralcross-sectional profile along said elongated length, thereby havingwidth, thickness, and length dimensions, wherein the average width is atleast 1.0 mm; wherein the average width is no more than 5.0 mm; whereinthe average thickness is at least 0.05 mm; wherein the average thicknessis no more than 0.2 mm; wherein the average length is at least 20 mm;wherein the average length is no more than 75 mm; wherein the averagewidth should exceed average thickness by a factor of at least 5; andwherein the average width should exceed average thickness by a factor nogreater than
 50. 41. The fibers of claim 37 wherein, in said pluralityof individual fiber bodies, said at least one synthetic polymer isselected from the group consisting of polyethylene, polypropylene,polyoxymethylene, poly(vinylidine fluoride), poly(methyl pentene),poly(ethylene-chlorotrifluoroethylene), poly(vinyl fluoride),poly(ethylene oxide), poly(ethylene terephthalate), poly(butyleneterephthalate), polyamide, polybutene, and thermotropic liquid crystalpolymers.
 42. The fibers of claim 37 wherein, in said plurality ofindividual fiber bodies, the average bendability of said fiber bodies isno less than 150 mN⁻¹*m⁻² and the average bendability of said fibers isno more than 2,000 mN⁻¹*m⁻².
 43. The fibers of claim 37 wherein saidindividual fiber bodies being substantially free of stress fractures andsubstantially non-fibrillatable when mechanically agitated within thematrix material to be reinforced, said fiber bodies having a generallyquadrilateral cross-sectional profile along said elongated length,thereby having width, thickness, and length dimensions, wherein theaverage width is at least 1.0 mm; wherein the average width is no morethan 3.0 mm; wherein the average thickness is at least 0.05 mm; whereinthe average thickness is no more than 0.15 mm; wherein the averagelength is at least 20 mm; wherein the average length is no more than 60mm; wherein the average width should exceed average thickness by afactor of at least 7; and wherein the average width should exceedaverage thickness by a factor no greater than
 40. 44. Fibers forreinforcing matrix materials, comprising: a plurality of individualfiber bodies having an elongated length defined between two opposingends and comprising at least one synthetic polymer, said individualfiber bodies being substantially free of stress fractures andsubstantially non-fibrillatable when mechanically agitated within thematrix material to be reinforced, said fiber bodies having a generallyquadrilateral cross-sectional profile along said elongated length,thereby having width, thickness, and length dimensions wherein theaverage width is no less than 1.0 mm; wherein the average width is nomore than 3.0 mm; wherein the average thickness is no less than 0.075mm; wherein the average thickness is no more than 0.15 mm; wherein theaverage length is no less than 20 mm; wherein the average length is nomore than 60 mm; wherein the average fiber width to thickness ratio isno less than 7; wherein the average fiber width to thickness ratio is nomore than 30; wherein said fiber bodies have a Young's modulus ofelasticity no less than 4 Giga Pascals; wherein said fiber bodies have aYoung's modulus of elasticity no more than 20 Giga Pascals; wherein saidfiber bodies have a tensile strength no less than 400 Mega Pascals;wherein said fiber bodies have a tensile strength of no more than 1,600Mega Pascals; wherein said fiber bodies have a minimum load carryingcapacity in tension mode no less than 20 Newtons per fiber body; whereinsaid fiber bodies have a minimum load carrying capacity in tension modeno greater than 1,000 Newtons per fiber body; wherein said fiber bodieshave an average square area to volume ratio no less than 10.5 mm⁻¹;wherein said fiber bodies have an average square area to volume ratio nomore than 42 mm⁻¹; wherein said fiber bodies have an average bendabilityno less than 150 mN⁻¹*m⁻²; and wherein said fiber bodies have an averagebendability no more than 2,500 mN⁻¹*m⁻².
 45. A matrix compositioncomprising said fibers of claim 37 and a matrix material selected fromthe group consisting of adhesives, asphalt, composite materials,plastics, elastomers, and hydratable cementitious materials.
 46. Thematrix composition of claim 45 wherein said matrix material is ahydratable cementitious composition (e.g. concrete, wet-mix and dry-mixshotcrete, dry mortar, mortar, cement paste) and said fibers comprisepolypropylene and polyethylene.
 47. The matrix composition of claim 45wherein said fibers are present in the matrix composition in the amountno less than 0.05% by volume and no greater than 10.0% by volume. 48.The fibers of claim 37, wherein said fibers are embedded in concrete,said concrete having compressive strength in the range of 15 to 40 MPawherein the average R_(e,3) value is between 20 and 60%, said concretehaving finishability whereby said embedded fibers do not substantiallypop out of said concrete; the average bendability of said fiber bodiesis no less than 100 mN⁻¹*m⁻² and the average bendability of said fibersis no more than 2,500 mN⁻¹*m⁻², wherein the average width of said fibersis no less than 1.0 mm; wherein the average width of said fibers is nomore than 3.0 mm; wherein the average thickness of said fibers is noless than 0.05 mm; wherein the average thickness of said fibers is nomore than 0.15 mm; wherein the average length is no less than 20 mm;wherein the average length of said fibers is no more than 70 mm; whereinsaid fiber bodies have a Young's modulus of elasticity no less than 4Giga Pascals; wherein said fiber bodies have a Young's modulus ofelasticity no more than 20 Giga Pascals; wherein said fiber bodies havea tensile strength no less than 400 Mega Pascals; wherein said fiberbodies have a tensile strength of no more than 1,600 Mega Pascals. 49.The fibers of claim 37 being embedded in a concrete floor, said concretehaving a compressive strength no less than 30 MPa and having acompressive strength no greater than 60 MPa; said fiber-embeddedconcrete floor having an average R_(e,3) value no less than 20% andhaving an average R_(e,3) value no more than 60%; said floor having afinishability wherein said embedded fibers do not substantially stickout of said concrete; the average bendability of said fiber bodies beingno less than 100 mN⁻¹*m⁻² and the average bendability of said fibersbeing no more than 2,500 mN⁻¹*m⁻²; said fibers having an average widthno less than 1.0 mm; said fibers having an average width no more than4.0 mm; said fibers having an average thickness is no less than 0.075mm; said fibers having an average thickness no more than 0.15 mm; saidfibers having an average length is no less than 20 mm; said fibershaving an average length no more than 60 mm; said fibers having aYoung's modulus of elasticity no less than 4 Giga Pascals; said fibershaving a Young's modulus of elasticity no more than 20 Giga Pascals;said fiber bodies having a tensile strength no less than 400 MegaPascals; said fiber bodies having a tensile strength no more than 1,600Mega Pascals.
 51. The fibers of claim 37 having a twist shape.
 52. Thematrix composition of claim 45 wherein said fibers are embedded in aconcrete slab.
 53. The matrix composition of claim 45 wherein saidfibers are embedded in shotcrete.